Flipping the Board for different perspective

You need time and experience just like you have said to get better at that. Playing OTB you won't be able to look at the position from your opponent's perspective. In the opening phase of the game there are already well known strwnghts and weaknesses for each side depending on the opening choice. You should know them before you decide to play a certain opening. As you play games experience is gained and you can often hear someone saying - I have played this many times before both as white and black. In that case a person doesn't even have to think (much or at all) about what is good or bad. Another way to bypass that would be to investigate some common openings you play and play it from the both sides. As for middlegame and endgame I dont know how to answer your question. There are some things you must to learn to get better. Look for material count, imbalances, weak squares, outposts, king safety and stuff like that. Also learn basic endgame principles, most common rook and pawn endgames, what is winning for which side. How to draw down a pawn, opposition, passed pawn and how to create one and many other thing. Best of luck!